Flow estimation for secondary air system

ABSTRACT

Methods and systems using model based and iterative calculations of mass flow throughout an internal combustion engine system. A secondary air injection valve is provided to selectively allow intake air to pass to the exhaust side of the engine system to aid in exothermic reaction with exhaust gasses exiting the engine for various purposes. The iterative calculations of mass flow include estimation of the mass flow through the secondary air injection valve.

BACKGROUND

Tightening emissions controls on internal combustion engines havecreated a range of incentives for new and different control systems,including focus on air path control. Exhaust gasses coming out of acombustion chamber are directed to various aftertreatment systems,including, for example and without limitation, three-way catalyst (TWC)devices, which convert toxic pollutants like carbon monoxide,hydrocarbons (such as partially or unburnt fuel), and nitrogen oxidesinto carbon dioxide, water, and/or nitrogen. When the TWC is cold, suchas at a cold start of the engine, the desired catalytic reactions willnot occur. One solution is to heat the TWC using, for example, anelectric heat element. Another solution is to operate the engine togenerate deliberately rich exhaust, and introduce ambient or fresh airinto the exhaust upstream of the TWC device to cause oxidation (burning)of the unburnt fuel so as to bring the TWC up to operating temperaturequickly. The introduction of fresh air, having higher oxygen levels thanthe exhaust, is referred to as secondary air injection (SAI).

One approach for introducing such fresh air is to pump fresh air intothe exhaust airstream at desired locations using, for example, a “smogpump” with a check valve to prevent reverse exhaust flow. This approachadds an extra system and associated control mechanism, making bothimplementation and control complex. Another approach is to introducecharged air (that is, pressurized air exiting a compressor upstream ofthe engine) through a secondary air valve into the exhaust flow, aprocess that can be controlled by the use of a flow sensor through whichthe secondary air flow passes. Such flow sensors add cost and introducean additional point of potential failure and/or error in the system, asflow sensors are subject to reduced flow and/or failure due to clogging.

These older approaches introduce cost and complexity. New andalternative approaches are desired for the introduction of secondaryair.

OVERVIEW

The present inventors have recognized, among other things, that aproblem to be solved is the need for new and/or alternative method forintroducing secondary air. Fresh air is introduced to the exhaustairstream from within the airflow exiting the compressor of aturbocharger used with the engine. The turbocharger may be a traditionalturbocharger, obtaining all power for use in the compressor from aturbine in the exhaust airstream. In some implementations, theturbocharger may be an E-Turbo device, which uses an electric motor toselectively provide additional torque to the compressor. Rather thanrelying on a flow sensor in line with the secondary air valve, thepresently disclosed methods estimate secondary air flow using a standardproduction sensor set, and implement system controls based on suchestimates.

A first illustrative, non-limiting example takes the form of a method ofestimating secondary air flow in an engine system, the engine systemincluding: a combustion engine having at least one combustion chamber,an intake manifold having intake manifold pressure and temperaturesensors and an exhaust manifold, a turbocharger having a compressor anda turbine configured to provide torque to the compressor, a charge aircooler (CAC), and an aftertreatment system including an environmentalcatalyst device (ECD), the engine system configured to receive ambientair, compress the ambient air in the compressor, cool the compressed airin the CAC, provide cooled compressed air to the intake manifold,combust a quantity of fuel with the cooled compressed air in the atleast one combustion chamber thereby generating exhaust, route theexhaust to the turbine, and route exhaust from the turbine to theaftertreatment system, the engine system also including a secondary airinjection (SAI) valve to controllably deliver compressed air from afirst location downstream of the compressor to the exhaust at a secondlocation, the SAI valve controlled by an SAI control signal; the methodcomprising: sensing an intake manifold pressure and an intake manifoldtemperature; sensing an ambient air pressure, a boost pressuredownstream of the CAC, and an engine speed; calculating a first pressureat the first location using the boost pressure and a CAC flow model;calculating a first temperature at the first location using a model ofthe compressor; calculating an exhaust manifold pressure; andcalculating a mass flow through the SAI valve from a model of the SAIvalve using the first pressure, the first temperature, the exhaustmanifold pressure, and the SAI control signal as inputs to the SAImodel.

Additionally or alternatively, a method as in the preceding example mayfurther comprise adjusting the SAI control signal in response to thecalculated mass flow through the SAI valve. Additionally oralternatively, a method as in the preceding example may further comprisedetermining that the engine has been started in a cold start condition;issuing a control signal to open the SAI valve; modulating a position ofthe SAI valve responsive to the calculated mass flow through the SAIvalve; determining that the ECD temperature is above an ECD temperaturethreshold; and issuing a control signal to close the SAI valve.Additionally or alternatively, the turbocharger includes an electricmotor configured to selectively provide torque to the compressor, andthe method also includes activating the electric motor of theturbocharger to provide torque to the compressor to raise pressure atthe first location. Additionally or alternatively, the turbochargerincludes an electric motor configured to selectively provide torque tothe compressor, and the method also includes determining whether apressure differential between the first location and the second locationis greater than a pressure differential threshold and, if not,activating the electric motor of the turbocharger to provide torque tothe compressor to raise pressure at the first location.

Additionally or alternatively, the first location is upstream of theCAC, and the second location is the exhaust manifold. Additionally oralternatively, the second location is downstream of the turbine andupstream of the ECD.

Additionally or alternatively, the steps of calculating the exhaustmanifold pressure and calculating the mass flow through the secondaryair valve is performed using an iterative calculation to solve thesemass flow equations: mass flow into the intake manifold plus mass of thequantity of fuel plus mass flow through the secondary air valve equalsturbine mass flow; turbine mass flow equals mass flow through theafter-treatment system.

Additionally or alternatively, the engine system further comprises awastegate positioned to allow exhaust to bypass the turbine, and theturbine mass flow includes mass flow passing through the turbine andmass flow bypassing the turbine via the wastegate.

Additionally or alternatively, the turbine is a variable geometryturbine (VGT).

Additionally or alternatively, the turbocharger includes an electricmotor configured to selectively provide torque to the compressor,further wherein, if the SAI valve is not closed, the method comprisesdetermining whether a pressure at the first location exceeds a pressureat the second location and, if not, activating the electric motor tosupply torque to the compressor and thereby increase pressure at thefirst location.

Additionally or alternatively, the aftertreatment includes a particulatefilter (PF), and the method further comprises: determining that the PFrequires refreshing; issuing a control signal to open the SAI valve toallow secondary air flow for use in refreshing the PF; modulating aposition of the SAI valve responsive to the calculated mass flow throughthe SAI valve; determining that the PF have been refreshed; and issuinga control signal to close the SAI valve.

Another illustrative, non-limiting example takes the form of a method ofcontrolling an engine, the engine having a combustion chamber with anintake manifold and an exhaust manifold, a turbocharger with acompressor and a turbine, an aftertreatment system including anenvironmental catalyst device (ECD) and a lambda sensor, and a secondaryair injection (SAI) valve controlled by an SAI control signal andconfigured to deliver charged air exiting the compressor at a firstlocation to a second location in the exhaust path between the exhaustmanifold and the ECD, the method comprising: determining the occurrenceof a transient engine operation and a temperature of the ECD below anECD temperature threshold; opening the SAI valve to enable secondary airinjection to the exhaust to facilitate heating the ECD; during thetransient engine operation, modulating the SAI control signal to adjusta position of the SAI valve using an open loop control strategy bycalculating a mass flow through the SAI valve from a model of the SAIvalve; determining an end of the transient engine operation while thetemperature of the ECD remains below the threshold; and upon the end ofthe transient engine operation, modulating the SAI control signal toadjust a position of the SAI valve using a closed loop control strategyby obtaining an output of the lambda sensor.

Additionally or alternatively, the engine also includes a charge aircooler (CAC) for cooling air exiting the compressor, and a throttlebetween the CAC and the intake manifold, a first sensor for sensing anintake manifold pressure, a second sensor for sensing an intake manifoldtemperature, a third sensor for sensing an ambient air pressure, afourth sensor for sensing a boost pressure downstream of the CAC andupstream of the throttle, and a fifth sensor for sensing an enginespeed; and the step of calculating a mass flow through the SAI valvefrom a model of the SAI valve comprises: sensing an intake manifoldpressure from the first sensor, an intake manifold temperature from thesecond sensor, an ambient air pressure from the third sensor, a boostpressure from the fourth sensor, and an engine speed from the fifthsensor; calculating a first pressure at the first location using theboost pressure and a CAC flow model; calculating a first temperature atthe first location using a model of the compressor; calculating anexhaust manifold pressure; and estimating a mass flow through the SAIvalve from a model of the SAI valve using the first pressure, the firsttemperature, the exhaust manifold pressure, and the SAI control signalas inputs to the SAI model. Additionally or alternatively the transientengine condition is a cold start of the engine.

Another illustrative and non-limiting example takes the form of a methodof estimating secondary air flow (SAI) in a controller for an enginesystem, the engine system including a combustion chamber coupledupstream to an intake manifold (IM) and downstream to an exhaustmanifold, a turbocharger having a compressor upstream of the intakemanifold and a turbine downstream of the exhaust manifold, a throttledownstream of the compressor and upstream of the IM, and an SAI flowpath including an SAI valve, the SAI flow path coupled from a firstlocation downstream of the compressor and upstream of the combustionchamber to a second location downstream of the compressor, the methodcomprising, with an SAI control signal provided to the SAI valve thatcauses the SAI valve to be at least partially open, the controllerperforming the following: obtaining an IM pressure and an IM temperaturefrom sensors in the IM; obtaining an ambient air pressure from anambient air pressure sensor, a boost pressure from a boost pressuresensor located upstream of the throttle, and an engine speed from anengine speed sensor; calculating a first pressure at the first locationusing the boost pressure; calculating a first temperature at the firstlocation using a compressor model; calculating an exhaust manifoldpressure; and estimating a SAI mass flow through the SAI flow path usinga model of the SAI valve, the IM pressure, the first pressure, the firsttemperature, the exhaust manifold pressure, and the SAI control signal.

Additionally or alternatively, a method may include determining theestimated SAI mass flow is lower than a target SAI mass flow and, inresponse, modifying the SAI control signal to open the SAI valve.Additionally or alternatively, a method may include determining theestimated SAI mass flow is lower than a target SAI mass flow and, inresponse, modifying operation of the turbocharger to increase the boostpressure. Another illustrative and non-limiting example takes the formof a method of controlling an engine system having a secondary air (SAI)flow path, comprising: identifying a cold start condition; opening anSAI valve in the SAI flow path; using a method as in any of thepreceding examples to estimate SAI mass flow; and modulating a controlsignal delivered to the SAI valve to increase or decrease SAI mass flowin response to the estimated SAI mass flow.

Another illustrative and non-limiting example takes the form of a methodof controlling an engine system having a secondary air (SAI) flow path,comprising: identifying a need to refresh a particulate filter; openingan SAI valve in the SAI flow path to allow secondary air flow for use inrefreshing the particulate filter; using a method as in any of thepreceding examples to estimate SAI mass flow; and modulating a controlsignal delivered to the SAI valve to increase or decrease SAI mass flowin response to the estimated SAI mass flow.

Another illustrative, non-limiting example takes the form of acombustion engine having at least one combustion chamber, an intakemanifold having intake manifold pressure and temperature sensors and anexhaust manifold, a turbocharger having a compressor and a turbineconfigured to provide torque to the compressor, a charge air cooler(CAC), and an aftertreatment system including an environmental catalystdevice (ECD), the engine system configured to receive ambient air,compress the ambient air in the compressor, cool the compressed air inthe CAC, provide cooled compressed air to the intake manifold, combust aquantity of fuel with the cooled compressed air in the at least onecombustion chamber thereby generating exhaust, route the exhaust to theturbine, and route exhaust from the turbine to the aftertreatmentsystem, the engine system also including a secondary air injection (SAI)valve to controllably deliver compressed air from a first locationdownstream of the compressor to the exhaust at a second location, theSAI valve controlled by an SAI control signal, and a controllerconfigured to perform a method of estimating SAI mass flow and/orcontrolling an engine as in any of the preceding method examples.

Still another illustrative, non-limiting example takes the form of acontroller for a combustion engine configured to perform a method as inany of the preceding method examples. Another illustrative, non-limitingexample takes the form of a non-transitory medium storing thereoninstructions for performing any of the preceding method examples.

This overview is intended to introduce the subject matter of the presentapplication. It is not intended to provide an exclusive or exhaustiveexplanation. The detailed description is included to provide furtherinformation about the present application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 shows an illustrative engine with a turbocharger and secondaryair injection; and

FIGS. 2-4 each show illustrative methods in block form.

DETAILED DESCRIPTION

FIG. 1 shows an illustrative engine with a turbocharger. The system 10includes an engine 20 having one or more cylinders 22, which receivesfuel from a fuel system 24, such as by one or more fuel injectors. Thefuel system 24 provides a known or set quantity of fuel for each firingof each cylinder 22, making for a determined quantity of fuel for eachfull firing sequence of the engine's cylinders. The speed of the engine,N_(E), represents the speed at which a full firing sequence takes place(whether or not all cylinders are active), and is sensed by an enginespeed sensor, such as, for example and without limitation, a variablereluctance sensor, a Hall effect sensor, or an optical sensor.

The airflow of the system includes fresh air intake passing through anair filter 30 and then going to a turbocharger 40 having a compressor 42and turbine 44 linked together by a drive shaft. The engine and/orvehicle will usually also include ambient air temperature and pressuresensors. The turbocharger 40 is configured to receive exhaust gasses atthe turbine 44, generating torque which is provided by a drive shaft tothe compressor 42. The turbocharger 40 may be, optionally, an electricassisted turbocharger (E-Turbo), having an electric motor 46 which canprovide additional torque to the compressor 42 when desired.

Air exiting the compressor 42 is considered the “charged” air flow,having been compressed, and it passes through a charge air cooler 50 toreduce temperature, and then to a throttle 52. To prevent turbochargersurge (reverse airflow through the compressor 42 which can be caused bypressure imbalances responsive to closing of the throttle 52), arecirculation valve 54 is provided to allow charged air to recirculateback to the compressor 42 input when possible surge conditions arepresent.

After passing through the throttle 52, the charged fresh air reaches theintake manifold of the engine 20. Prior to entering the intake manifoldthe charged fresh air may be mixed with recirculated exhaust gasses thatpass through a high-pressure exhaust gas recirculation (HPEGR) valve 62,which will typically also pass the recirculated gas through an EGRCooler (not shown). The recirculated exhaust gas aids in reducingcombustion temperatures in the engine 20, reducing certain noxiousemissions. Alternatively or additionally, the system may include alow-pressure exhaust gas recirculation (LPEGR) valve, shown at 64 and anassociated EGR cooler (not shown).

HPEGR 62 is more typical of diesel engines, while LPEGR 64 is morecommon with gasoline engines. Either or both may be included or omitted,as desired. The present disclosure is mainly directed towardimplementation in a gasoline engine, however, the systems and methodsfor estimating secondary air flow may also be used in a diesel engine,or in engines burning other fuels. Such combustion engines may serve asthe only power source in a vehicle, or may be combined with additionalpower systems, such as electric drive systems in a hybrid vehicle, ifdesired.

The intake manifold typically includes each of an intake manifoldpressure sensor and an intake manifold temperature sensor. Air enteringthe intake manifold then enters the combustion chambers 22. Duringcombustion the charged air mass is combined with the fuel mass, m_(F).Exhaust gasses leave the engine at an exhaust manifold. Exhaust gassesare then directed to the turbine 44, which obtains torque/force from theexhaust gas that is in turn applied via the drive shaft to thecompressor 42. In some examples the speed of rotation of theturbocharger drive shaft is a measured variable, referred to asturbocharger speed. A turbocharger speed sensor may be provided in someexamples, but is not always present, and may take the form of, forexample and without limitation, a variable reluctance sensor, a Halleffect sensor, or an optical sensor.

A wastegate 66 allows venting of exhaust gas without passing through theturbine 44 to control turbocharger speed. Rather than a wastegate 66, avariable geometry turbine (VGT) may be used to manage gasses enteringthe turbine 44, if desired.

Gasses exiting the system either via the turbine 44 or the wastegate 46go to an aftertreatment system 70 where various aftertreatment devicesmay remove or reduce pollutants. An environmental catalyst device (ECD)72 is included in the aftertreatment system 70, and is of particularnote in the present innovation. An ECD may take the form of a three-waycatalytic converter (TWC), which would be typical for a gasoline engine,or a selective catalytic reduction device (SCR), which would be typicalfor a diesel engine.

A TWC may include a substrate brick coated with a washcoat containingthe catalytic material. To convert carbon monoxide, hydrocarbons, andnitrous oxides into carbon dioxide, water, and nitrogen gas, the TWCneeds to be at or above a threshold temperature, typically in the rangeof 400 degrees Celsius (though this may vary with the particular TWC).When the TWC is too cool, such as at engine startup, the TWC will notperform its function.

Most SCR devices inject urea to form ammonia in an SCR bed. To convertthe urea to ammonia and cause reaction with pollutants that are desiredto be reduced also requires the SCR bed to be at or above a thresholdtemperature, with desirable targets exceeding 250 degrees Celsius, moreoften over 300 degrees Celsius. When the SCR bed is too cool, such as atengine startup (“cold start”), the SCR will fail to perform itsfunction.

An ECD may take other forms for use with other fuels, and may havedifferent needs as well. For example, with a natural gas engine, methaneemissions may need to be controlled, but may require even highertemperatures for catalytic conversion. It may be useful in someimplementations to have more than one ECD at different locations toallow for different temperatures to optimize different reactions. Thetemperatures ranges noted above are merely illustrative, and may varywith particular fuels, different ECD types, and/or other factors. In anyevent, in some examples, raising ECD bed temperature quickly enablesbetter conformity to emissions standards.

A cold start, as used herein, may be defined in various ways. In someexamples, “cold start” may be determined by whether the engine startsafter at least a minimum period of non-operation, where the minimumperiod of non-operation may be in the range of 15 minutes to 7 hours. A“cold start” may instead by determined by whether the engine startswhile the ECD bed is at a temperature that is below a cut-off forcorrect operation of the ECD, where the cutoff temperature is in therange of about 50 to about 400 degrees Celsius.

One or more lambda sensors or universal exhaust gas oxygen (UEGO)sensors 74 (collectively referred to as Lambda sensors herein) may beprovided, including, for example and without limitation, at a locationdownstream of the aftertreatment system 70, and/or upstream of theturbine 44, as desired. A “cold start” may instead refer to a status ofthe Lambda sensor condition, where the minimum operating temperature ofthe Lambda sensor 74 will typically be in the range of about 300 to 350degrees Celsius. Until the Lambda sensor 74 reaches its operatingtemperature, the Lambda sensor 74 output will be unavailable orunreliable, and a model-based mass flow is used rather than Lambdasensor 74 outputs. In some examples, as shown in FIG. 4 below, a “coldstart” may be the basis for performing certain operations, and theunderlying control over such operations can vary in response to Lambdasensor 74 operational status.

The measured oxygen concentration from the Lambda sensor can be used todetermine air to fuel ratio in the engine 20, for example, and is oftenused to determine adjustments to the air to fuel ratio which can beimplemented by modifying fuel input and/or operation of the turbocharger40. One problem with Lambda sensors 74 is that the sensor output issubject to sensor lag (delayed response), making the Lambda sensor 74 apoor indicator of current conditions when operations are changing(transient). Another issue at cold start is that the Lambda sensor 74operating range requires elevated temperatures, making the Lambda sensoroutput temporarily unusable during cold starting.

The system may also include a particulate filter 76, such as a diesel orgasoline particulate filter, or other particulate filters adapted forother fuels, as is known in the art.

A secondary air injection (SAI) air path is also provided, including anSAI valve 60. The SAI valve 60 may be a non-return valve to preventbackflow of exhaust. SAI can be used to deliver additional oxygen to theexhaust gas flow when desired, for example, to cause post-oxidation(“post-combustion”) reaction with exhaust gas constituents, inparticular, the carbon monoxide and unburned hydrocarbons that areproduced during cold start. Not only do these reactions reduce thepresence of the harmful exhaust components, but the reactions are alsoexothermic, creating heat that helps bring the ECD bed up to itsoperating temperature. In the example shown, the SAI path starts at afirst location, downstream of the compressor 42 and upstream of the CAC50, and delivers the fresh air to a second location which may be at theexhaust manifold of the engine 20 (as shown with the heavy broken linein FIG. 1 ). Alternatively, the SAI path may bring the fresh air intothe exhaust flow at any location downstream of the exhaust manifold andupstream of the turbine. Another alternative would be for the secondlocation to be located at 61, downstream of the turbine 44 and wastegate66 (if present), and upstream of the aftertreatment 70 and ECD 72. Eachline between elements in the air path, including the broken line shownfor the SAI air path, may represent a tube, channel, pipe or othersuitable air passageway.

Small boxes are shown throughout the figure representing temperature andpressure at various locations:

T₀, and p₀ represent the ambient air temperature and air pressure

T_(21a), and p_(21a) represent pressure and temperature at the outlet ofthe compressor 42;

T₂, and p₂ represent pressure and temperature at the intake manifold;

T₃, and p₃ represent pressure and temperature at the exhaust manifold;and

T₄, and p₄ represent pressure and temperature at the outlet of theturbine 44.

In a production system, the ambient air temperature and pressure (T₀,and p₀), and the intake manifold pressure and temperature (T₂ and p₂)may be measured parameters, and other pressures and temperatures areestimated, calculated and or inferred using a model of the system andother characteristics. Engine speed (N_(E)) will also be known, as isthe mass input via the fuel injectors of the engine 20, and the outputof the lambda sensor. In some examples, the turbocharger speed may bemeasured.

In the illustrative system, one additional pressure sensor, p₂₁ may beprovided at the location shown as part of the production system,obtaining pressure downstream of the CAC 50 and upstream of the throttle52. The p₂₁ sensor is used to compute p_(21a) using a CAC restrictionmodel. The temperature T_(21a) would be computed using a compressortemperature rise model, which in turn uses the computed p_(21a) value,T₀, and p₀.

In a system under test, such as a build/system used for modelling,additional sensors may be present throughout the system for capturingtemperatures, pressures or other parameters as desired. The addedsensors aid in the development and calibration of models used inproduction systems to estimate, calculate or infer the variouspressures, temperatures, mass flows, etc. as needed. For example, thecompressor temperature rise model and CAC restriction model can each bedeveloped using additional sensors for a system under test to directlysense T_(21a) and p_(21a).

The operation in general is controlled by an engine control unit (ECU)80. The ECU 80 may include a microcontroller or microprocessor, asdesired, or other logic/memory, application specific integrated circuit(ASIC), etc., with associated memory for storing observedcharacteristics as well as operational instruction sets in anon-transitory medium, such as a Flash or other memory circuitry. TheECU 80 will be coupled to various actuators throughout the system, aswell as to the provided sensors, to obtain data and issue controlsignals as needed. The ECU may couple to other vehicle control systemssuch as by a controller area network (CAN) bus or other wired orwireless link. Multiple ECUs 80 may be present, such as by having aseparate ECU dedicated to controlling the turbocharger 40.

Mass flow through the system can be understood by taking one piece at atime. The flows into and out of the exhaust manifold from the combustionchambers and secondary air valve may be represented as shown in Formula1:0=m _(eng)(p ₂ ,p ₃ ,T ₂ ,N _(e),Cams)+m _(f) +m _(SAI)(p _(21a) ,p ₃ ,T_(21a) ,u _(SAI))−m _(HPEGR)(p ₂ ,p ₃ ,T ₃ ,u _(HPEGR))−m _(turbine)(p ₃,p ₄ ,T ₃ ,N _(t))−m _(wg)(p ₃ ,p ₄ ,T ₃ ,u _(WG))  {1}Where the function m_(eng) is developed using a system under test as afunction of the intake manifold pressure and temperature, the pressurein the exhaust manifold, the engine speed, and the cam shaft positions(C_(AMS)), such as variable lift or phasing, (the equation can bemodified to include any other signal that influences the charge airflow), and outputs the mass of charge air flowing into the engine. Massflow of the fuel (m_(f)) is a function of the settings of the fuelsystem input. The secondary air flow mass function, m_(SAI), is afunction of the pressures p_(21a) and p₃, temperature T_(21a), and thecontrol signal for the SAI valve, u_(SAI), and is a flow model for theSAI valve that would be developed in a system under test. The highpressure EGR mass flow, m_(HPEGR), is a function of p₂, p₃, T₃, and theHP EGR control signal, u_(HPEGR). The mass flow through the turbine andwastegate are each separated in Formula 1. Specifically, the mass flowthough the turbine, m_(turbine) is the function of p₃, p₄, T₃, and theturbine speed, N_(t), (which may itself be measured or modelled, asdesired). Mass flow through the wastegate, m_(wg), is a function of p₃,p₄, T₃, and the wastegate position or control signals, u_(wg).

The combined mass flow through the turbine and wastegate, must be equalto the mass flow into the exhaust system, as shown by Formula 2:0=m _(turbine)(p ₃ ,p ₄ ,T ₃ ,N _(t))+m _(wg)(p ₃ ,p ₄ ,T ₃ ,u _(WG))−m_(aft)(p ₄ ,p ₀ ,T ₄ ,u _(LPEGR))  {2}The function, m_(aft), is the mass flow through the exhaust systembefore any low pressure (LP) EGR loop. As shown, m_(aft) is a functionof the post-turbine pressure p₄ and temperature t₄, ambient pressure p₀,and the LP EGR valve position or valve control signal, u_(LPEGR). Themodel for mass flow through the low pressure EGR, m_(LPEGR) would bedeveloped using a system under test, and relies on pressures p₄ and p₀,and temperature T₄, along with the LPEGR control signal, u_(LPEGR).

For a system with VGT, the turbine model would be replaced with a flowmodel that includes relationship of the vane position, uVGT and thewastegate model could be removed, substituting the following in place ofm_(wg) in formulae 1 and 2:m _(turbine)(p ₃ ,p ₄ ,T ₃ ,N _(t) ,u _(VGT))

Equations 1-2 come from the same system and account for each mass flowinput and output of the system across a controlled volume. These twononlinear equations are sufficient to uniquely solve the flow balancefrom a standard sensor set. Any iterative solver, such as aGauss-Newton, Newton-Raphson, or iterated Kalman Filter can be used tosolve the two unknown pressures p₃ and p₄, and therefore calculate eachmass flow and extract from the mass flows the quantity of mass flowingthrough the SAI valve. SAI valve position can then be modulated (openedand closed based on a target value for the SAI flow) using any suitablecontrol method, such as proportional-integral-derivative (PID) control,model-based control such as model predictive control (MPC), etc.Additionally or alternatively, E-Turbo control or torque may bemodified. In still other examples, settings of the turbochargerwastegate and/or VGT may be modified, for example, to increase chargeair pressure to increase SAI flow.

The formula set can be revised to account for other layouts, as desired.

With the system as shown in FIG. 1 , it may be noted that the cold startengine condition in which SAI would be used may be an idle (or highidle) state. In some examples, to augment the operation of thecompressor during the idle state, the E-Turbo 46 may be used to increasethe speed of the compressor, raising boost pressure p₂₁ and pressurep_(21a) in turn, and thereby affecting (increasing) SAI mass flow.

FIGS. 2-4 each show illustrative methods in block form. Starting withFIG. 2 , a cold start is identified, as indicated at 100. A cold startmay be identified by determining how much time has passed betweencessation of prior engine operation and initiation of engine operation,where if more than a selected time duration (for example in the range of30 minutes to 7 hours) has passed, a cold start is identified. A coldstart may be identified in other examples by reference to a sensedtemperature of the ECD, the ECD bed, or a Lambda sensor, where if thetemperature of one or more of these elements is less than an operationalthreshold (typically 300 Celsius or more, though other values can beused depending on preferences, fuel type, catalyst type, and theparticular implementation), a cold start is identified. Booleancombination of such factors may be used, for example, a cold start maybe identified if more than 30 minutes have passed since the engine waslast in use and the ECD bed temperature is below the operationalthreshold.

Having identified the cold start, the SAI valve is opened, as indicatedat 102. SAI mass flow is next calculated at 104, using for example,equations 1-3 above in an iterative solver. The SAI valve position ismodulated as indicated at 106, for example, to open the SAI valveposition if SAI mass flow is below a determined target, or to close theSAI valve if the SAI mass flow is above a determined target, bymodifying an SAI valve control signal. It may be noted here that withthe method described, no flow sensor is needed for the SAI valve or SAIsystem to calculate the mass flow therethrough.

Next, at block 108, the method determines whether continued operation isneeded by determining whether the ECD temperature (or ECD bedtemperature) is above an operating threshold. The actual threshold mayvary by installation and ECD design. If the ECD temperature is not abovethe threshold at 108, the method returns to block 104, for a nextiteration of the method. If the ECD temperature has reached or exceededthe threshold at block 108, the method next closes the SAI valve at 110,as further SAI flow is not required for warming the ECD and/orpollutants from the exhaust flow, and the method ends.

Block 120 is also shown in in the illustrative method, and may beoperable at any point in the method. In block 120, a comparison of thepressure upstream of the SAI valve to the pressure downstream of the SAIvalve is made to find a pressure differential. For example the pressurein the exhaust manifold may be compared to the pressure at thecompressor outlet. Depending on layout, other comparisons can be made.If the pressure differential is below a threshold, more boost pressureis desired from the compressor, and so the E-Turbo motor is activated toprovide additional torque to the compressor, increasing compressor speedand raising the pressure upstream of the SAI valve. Block 120 may beomitted for systems that do not have an E-Turbo motor. If the comparisonis to pressure in the exhaust manifold, the pressure in the exhaustmanifold may vary widely, and so any of a minimum pressure, a maximumpressure, or an average pressure at the exhaust manifold may be used incalculating the pressure differential.

In an example, activation of the E-Turbo may be performed using thefollowing approach. First, the control system may measure and/orcalculate the pressures that are relevant to SAI mass flow. Note, forexample, as shown above, that SAI mass flow is a function of thepressures p_(21a) and p₃, temperature T_(21a), and the control signalfor the SAI valve, u_(SAI). In an example, addition of torque to theturbocharger by the electric motor of the E-Turbo is activated bycalculating whether the pressure differential is above or below athreshold from the following:

If p_(21a)−p₃<X, add torque

Else, reduce E-Turbo torque to Standard

Where the value for X may be a function of T_(21a), recognizing thatsuch a temperature impacts the SAI mass flow, and where “Standard” isthe E-Turbo torque input calculated through any other system controlmethods. For example, a system may include a control sub-function usedto calculate the E-Turbo torque that is desired relative to the enginecylinders, without consideration of SAI mass flow. In another example,when SAI mass flow is desired, the system may again compare p_(21a) andp₃ and determine whether to open or close the wastegate, or adjust vanesettings with the VGT, to increase power to the compressor of theturbocharger and thereby increase p₂₁ and p_(21a).

Any condition for which a response of heating a portion of the systemusing SAI may serve at block 100 to initiate the process of FIG. 2 ,which an adjustment made to block 108 to determine when the SAI processhas reached a completion point.

In another example, an engine status or condition other than “coldstart” may be used at block 100 to initiate the method. For example, ina system having an ammonia/NOx sensor in the exhaust flow, the detectionof excess ammonia can be indicative of ammonia slip associated withexcess urea introduction on a selective catalytic reduction (SCR) deviceand/or low SCR bed temperature. When excess ammonia is detected, aspecial mode to increase SCR bed temperature can be called such as bydetecting SCR bed temperature and determining that an increase in SCRbed temperature is needed (within a maximum limit) to a new SCR bedtemperature target, which would serve as the ECD temperature thresholdin block 108. For example, the new SCR bed temperature target may be setas some quantity of degrees Celsius (20 degrees C., for example)increase from whatever the temperature is at the time the excess ammoniaslip is found. Having detected excess ammonia slip, and having set a newSCR bed temperature target, the method of FIG. 2 can be used to open theSAI valve at 102, calculate SAI mass flow (potentially with activationof the E-Turbo at 120), modulation of SAI valve position at 106, and thetemperature target check at 108 to determine if the SCR bed temperaturehas reached the new SCR bed temperature target.

FIG. 3 illustrates a special mode that can be used for refreshing aparticulate filter (PF). The PF captures and stores exhaust soot inorder to reduce emissions. The PF may be designed for a specific fuel,and may take the form of, for example and without limitation, a dieselparticulate filter or a gasoline particulate filter, or any other fuelparticulate filter. Trapped soot may occasionally or periodically beburned off using an operation as show in FIG. 3 . First, as shown at200, it is determined whether a PF refresh is needed, such as bydetermining how much time has passed since a last refresh, or bymonitoring the quantity of soot in the PF, the quantity of soot passingby the PF, or by determining a flow resistance at the PF. If PF refreshis needed at 200, the method opens the SAI valve at 202 to increase theamount of oxygen available in the exhaust, and may, as indicated at 204initiate a rich combustion routine by increasing fuel injection. Thecombination of fresh air injection via the SAI, and the rich combustionstate, will lead to burn off in the aftertreatment. The SAI mass flow iscalculated at 210, and the calculated mass flow is used to modulate SAIposition at 212, similar to block 106, above. After a period of time haspassed, or in response to sensing a temperature at the PF has reached orexceeded a threshold (for example, above a threshold for a period oftime), PF refresh complete is declared at 214, and the SAI valve isclosed as indicated at 216.

FIG. 4 illustrates another method for managing a cold start. Here, thecold start is identified at 300, similar to block 100 in FIG. 2 . Atblock 302, the SAI valve is opened by issuing a control signal to theSAI valve. Next the method determines whether the Lambda sensor isoperating 304. Block 304 may include several considerations, includingin some examples, whether the temperature of the Lambda sensor is in anoperational range. Block 304 may also contemplate whether the system isoperating in a transient state; some operators or systems may, forexample, vary the engine speed following cold start. If the Lambdasensor is not operational due to transient conditions or the sensor notbeing in an operational range, the method continues to block 310 inwhich SAI mass flow is calculated using a method as discussed aboverelative to Equations 1-2. Optionally, the calculated mass flow at block310, or the pressures that are calculated for purposes of block 310, maybe used to determine whether to activate the E-Turbo motor, as indicatedat 312. The SAI valve position is then modulated as indicated at 314 by,for example, issuing a control signal to open the valve if SAI mass flowis less than desired, or to close the valve if SAI mass flow is greaterthan desired. Control in block 314 may be performed by the use of, forexample, PID, MPC, or any other suitable control algorithm.

Next, the method determines whether the ECD temperature remains below athreshold for ECD operation, as indicated at 330. If ECD temperatureremains below threshold, then the method returns to block 304 to againcheck on whether the Lambda sensor is operable. If the ECD temperaturehas reached its threshold, the method may proceed to closing the SAIvalve at 332 and ending.

Returning to block 304, if the Lambda sensor is in an operational state(whether coming from block 302 or block 330), the method next obtainsthe Lambda sensor output at 320, and modulates SAI valve position at 322to either increase the mass flow through the SAI (if the Lambda sensorindicates low to no oxygen in the exhaust), or to decrease the mass flowthrough the SAI (if the Lambda sensor indicates excess oxygen in theexhaust). Again, control may be PID, MPC, or any other suitable control.In an example, if the Lambda output indicates low or no oxygen in theexhaust and the SAI valve position or control signal is already at amaximum opening of the SAI valve, the E-Turbo may be activated.

In some examples, the SAI mass flow will still be calculated after theLambda sensor is operational as indicated at 326. For example, SAI massflow calculations may be used to determine whether the boost pressure issufficient to achieve the desired effect (a desired quantity of SAI massflow) in the aftertreatment system. Again, using the exhaust manifoldpressure and compressor outlet pressures as a simple example, if thecompressor outlet pressure is not high enough to ensure mass flowthrough the SAI valve to the exhaust manifold, the E-Turbo motor may beactivated to add further torque to the compressor to thereby increasecompressor outlet pressure.

It may be noted that FIG. 4 illustrates two different conditions forcontrolling the E-Turbo in association with the SAI function. In one,when the Lambda sensor identifies low oxygen content with the SAI valvefully open, it may be inferred that SAI mass flow is inadequate, andincreased charge air pressure is desired. If the SAI valve is partiallyopen and low oxygen content is sensed by the Lambda sensor, in someexamples, the low oxygen content may prompt a change to the SAI valvecontrol signal to fully, or more fully, open the SAI valve. In additionor alternatively, the E-Turbo is activated to provide additional chargepressure and hence additional SAI mass flow (and/or the settings of awastegate and/or VGT may be modified to increase compressor power and/orturbocharger speed to increase charge pressure). In another, when SAImass flow is estimated, using the analytical process of Equations 1 and2, to be below a desired level, due to insufficient pressuredifferential between p₂₁ and p₃, the E-Turbo can be called upon toincrease p₂₁. Further, if the pressure differential is deemedinsufficient, settings of a wastegate and/or VGT may be modified toincrease compressor power and/or turbocharger speed to increase chargepressure).

In some examples, blockage or failure of the SAI valve may beidentified. In one example, with the Lambda sensor operational(preferably operating in its acceptable temperature range and absenttransient conditions), the SAI valve control signal may be changed toopen the valve. It would then be expected that the Lambda sensor wouldidentify an increase in oxygen in the exhaust flow. If no change inoxygen content is identified, the system may confirm that the pressuredifferential between p₂₁ and p₃ exceeds at least a minimum threshold(and if not, may increase boost pressure using any of the above notedmethods via wastegate, VGT, and/or E-Turbo operation), and then concludethat the SAI valve and/or SAI flow path is blocked or not functioningcorrectly.

In a further example, an SAI effect model may be constructed using atest stand, for example, to estimate changes in Lambda sensor outputresponsive to select levels of SAI mass flow under select engineconditions. Then, during operation, the SAI valve may be opened and theabove methods (such as using Equations 1 and 2) are used to estimate SAImass flow for inputting to the SAI effect model. Lambda sensor output isthen monitored to confirm a match to modeled effects; if no match isfound, the system may record a possible issue with the SAI valve and/orSAI flow path.

Each of these non-limiting examples can stand on its own, or can becombined in various permutations or combinations with one or more of theother examples. The above detailed description includes references tothe accompanying drawings, which form a part of the detaileddescription. The drawings show, by way of illustration, specificembodiments. These embodiments are also referred to herein as“examples.” Such examples can include elements in addition to thoseshown or described. However, the present inventors also contemplateexamples in which only those elements shown or described are provided.Moreover, the present inventors also contemplate examples using anycombination or permutation of those elements shown or described (or oneor more aspects thereof), either with respect to a particular example(or one or more aspects thereof), or with respect to other examples (orone or more aspects thereof) shown or described herein. In the event ofinconsistent usages between this document and any documents soincorporated by reference, the usage in this document controls. In thisdocument, the terms “a” or “an” are used, as is common, to include oneor more than one, independent of any other instances or usages of “atleast one” or “one or more.” Moreover, in the claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic or optical disks,magnetic cassettes, memory cards or sticks, random access memories(RAMs), read only memories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims.

Also, in the above Detailed Description, various features may be groupedtogether to streamline the disclosure. This should not be interpreted asintending that an unclaimed disclosed feature is essential to any claim.Rather, innovative subject matter may lie in less than all features of aparticular disclosed embodiment. Thus, the following claims are herebyincorporated into the Detailed Description as examples or embodiments,with each claim standing on its own as a separate embodiment, and it iscontemplated that such embodiments can be combined with each other invarious combinations or permutations. The scope of the protection shouldbe determined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A method of estimating secondary air flow in anengine system, the engine system including: a combustion engine havingat least one combustion chamber, an intake manifold having intakemanifold pressure and temperature sensors and an exhaust manifold, aturbocharger having a compressor and a turbine configured to providetorque to the compressor, a charge air cooler (CAC), and anaftertreatment system including an environmental catalyst device (ECD),the engine system configured to receive ambient air, compress theambient air in the compressor, cool the compressed air in the CAC,provide cooled compressed air to the intake manifold, combust a quantityof fuel with the cooled compressed air in the at least one combustionchamber thereby generating exhaust, route the exhaust to the turbine,and route exhaust from the turbine to the aftertreatment system, theengine system also including a secondary air injection (SAI) valve tocontrollably deliver compressed air from a first location downstream ofthe compressor to the exhaust at a second location, the SAI valvecontrolled by an SAI control signal; the method comprising: sensing anintake manifold pressure and an intake manifold temperature; sensing anambient air pressure, a boost pressure downstream of the CAC, and anengine speed; calculating a first pressure at the first location usingthe boost pressure and a CAC flow model; calculating a first temperatureat the first location using a model of the compressor; calculating anexhaust manifold pressure; and calculating a mass flow through the SAIvalve from a model of the SAI valve using the first pressure, the firsttemperature, the exhaust manifold pressure, and the SAI control signalas inputs to the model of the SAI valve.
 2. The method of claim 1,further comprising adjusting the SAI control signal in response to thecalculated mass flow through the SAI valve.
 3. The method of claim 1further comprising: determining that the combustion engine has beenstarted in a cold start condition; issuing a control signal to open theSAI valve; modulating a position of the SAI valve responsive to thecalculated mass flow through the SAI valve; determining that an ECDtemperature is above an ECD temperature threshold; and issuing a controlsignal to close the SAI valve.
 4. The method of claim 3 wherein theturbocharger includes an electric motor configured to selectivelyprovide torque to the compressor, and the method also includesactivating the electric motor of the turbocharger to provide torque tothe compressor to raise a pressure at the first location.
 5. The methodof claim 3 wherein the turbocharger includes an electric motorconfigured to selectively provide torque to the compressor, and themethod also includes determining whether a pressure differential betweenthe first location and the second location is greater than a pressuredifferential threshold and, if not, activating the electric motor of theturbocharger to provide torque to the compressor to raise a pressure atthe first location.
 6. The method of claim 1 wherein the first locationis upstream of the CAC, and the second location is the exhaust manifold.7. The method of claim 1 wherein the second location is downstream ofthe turbine and upstream of the ECD.
 8. The method of claim 1, whereinthe steps of calculating the exhaust manifold pressure and calculatingthe mass flow through the secondary air infection valve is performedusing an iterative calculation to solve these mass flow equations: massflow into the intake manifold plus mass of the quantity of fuel plusmass flow through the secondary air infection valve equals turbine massflow; turbine mass flow equals mass flow through the aftertreatmentsystem.
 9. The method of claim 8 wherein the engine system furthercomprises a wastegate positioned to allow exhaust to bypass the turbine,and the turbine mass flow includes mass flow passing through the turbineand mass flow bypassing the turbine via the wastegate.
 10. The method ofclaim 8 wherein the turbine is a variable geometry turbine (VGT). 11.The method of claim 1, wherein the turbocharger includes an electricmotor configured to selectively provide torque to the compressor,further wherein, if the SAI valve is not closed, the method comprisesdetermining whether a pressure at the first location exceeds a pressureat the second location and, if not, activating the electric motor tosupply torque to the compressor and thereby increase the pressure at thefirst location.
 12. The method of claim 1, wherein the aftertreatmentsystem includes a particulate filter (PF), and the method furthercomprises: determining that the PF requires refreshing; issuing acontrol signal to open the SAI valve to allow secondary air flow for usein refreshing the PF; modulating a position of the SAI valve responsiveto the calculated mass flow through the SAI valve; determining that thePF has been refreshed; and issuing a control signal to close the SAIvalve.
 13. A method of controlling an engine, the engine having acombustion chamber with an intake manifold and an exhaust manifold, aturbocharger with a compressor and a turbine, an aftertreatment systemincluding an environmental catalyst device (ECD) and a lambda sensor,and a secondary air injection (SAI) valve controlled by an SAI controlsignal and configured to deliver charged air exiting the compressor at afirst location to a second location in the exhaust path between theexhaust manifold and the ECD, the method comprising: determining anoccurrence of a transient engine operation and a temperature of the ECDbelow an ECD temperature threshold; opening the SAI valve to enablesecondary air injection to the exhaust to facilitate heating the ECD;during the transient engine operation, modulating the SAI control signalto adjust a position of the SAI valve using an open loop controlstrategy by calculating a mass flow through the SAI valve from a modelof the SAI valve; determining an end of the transient engine operationwhile the temperature of the ECD remains below the threshold; and uponthe end of the transient engine operation, modulating the SAI controlsignal to adjust a position of the SAI valve using a closed loop controlstrategy by obtaining an output of the lambda sensor.
 14. The method ofclaim 13, wherein the engine also includes a charge air cooler (CAC) forcooling air exiting the compressor, and a throttle between the CAC andthe intake manifold, a first sensor for sensing an intake manifoldpressure, a second sensor for sensing an intake manifold temperature, athird sensor for sensing an ambient air pressure, a fourth sensor forsensing a boost pressure downstream of the CAC and upstream of thethrottle, and a fifth sensor for sensing an engine speed; and the stepof calculating a mass flow through the SAI valve from a model of the SAIvalve comprises: sensing an intake manifold pressure from the firstsensor, an intake manifold temperature from the second sensor, anambient air pressure from the third sensor, a boost pressure from thefourth sensor, and an engine speed from the fifth sensor; calculating afirst pressure at the first location using the boost pressure and a CACflow model; calculating a first temperature at the first location usinga model of the compressor; calculating an exhaust manifold pressure; andestimating a mass flow through the SAI valve from a model of the SAIvalve using the first pressure, the first temperature, the exhaustmanifold pressure, and the SAI control signal as inputs to the model ofthe SAI valve.
 15. The method of claim 13, wherein the transient enginecondition is a cold start of the engine.
 16. A method of estimatingsecondary air flow (SAI) in a controller for an engine system, theengine system including a combustion chamber coupled upstream to anintake manifold (IM) and downstream to an exhaust manifold, aturbocharger having a compressor upstream of the intake manifold and aturbine downstream of the exhaust manifold, a throttle downstream of thecompressor and upstream of the IM, and an SAI flow path including an SAIvalve, the SAI flow path coupled from a first location downstream of thecompressor and upstream of the combustion chamber to a second locationdownstream of the combustion chamber, the method comprising, with an SAIcontrol signal provided to the SAI valve that causes the SAI valve to beat least partially open, the controller performing the following:obtaining an IM pressure and an IM temperature from sensors in the IM;obtaining an ambient air pressure from an ambient air pressure sensor, aboost pressure from a boost pressure sensor located upstream of thethrottle, and an engine speed from an engine speed sensor; calculating afirst pressure at the first location using the boost pressure;calculating a first temperature at the first location using a compressormodel; calculating an exhaust manifold pressure; and estimating a SAImass flow through the SAI flow path using a model of the SAI valve, theIM pressure, the first pressure, the first temperature, the exhaustmanifold pressure, and the SAI control signal.
 17. The method of claim16, further comprising determining the estimated SAI mass flow is lowerthan a target SAI mass flow and, in response, modifying the SAI controlsignal to open the SAI valve.
 18. The method of claim 16, furthercomprising determining the estimated SAI mass flow is lower than atarget SAI mass flow and, in response, modifying operation of theturbocharger to increase the boost pressure.
 19. A method of controllingan engine system having a secondary air (SAI) flow path, comprising:identifying a cold start condition; opening an SAI valve in the SAI flowpath; using the method of claim 16 to estimate SAI mass flow; andmodulating a control signal delivered to the SAI valve to increase ordecrease SAI mass flow in response to the estimated SAI mass flow.
 20. Amethod of controlling an engine system having a secondary air (SAI) flowpath, comprising: identifying a need to refresh a particulate filter;opening an SAI valve in the SAI flow path to allow secondary air flowfor use in refreshing the particulate filter; using the method of claim16 to estimate SAI mass flow; and modulating a control signal deliveredto the SAI valve to increase or decrease SAI mass flow in response tothe estimated SAI mass flow.